Optical isolators are used in optical communications systems and optical networks to eliminate or reduce reflected light waves. The presence of reflected light waves in such systems and networks are problematic and may result in significant problems, disadvantages and instabilities, especially when reflected light waves reach or reenter a laser source, such as a semiconductor laser, or optical amplifier.
Conventional optical isolators were developed to eliminate or minimize the presence of reflected light waves. Unfortunately, the manufacture and implementation of conventional optical isolators is complicated, unreliable, expensive and fraught with difficulties and disadvantages.
The implementation of conventional optical isolators is often cumbersome and expensive. For example, conventional optical isolators may use non-reciprocal Transverse Electric (“TE”) mode converters and non-reciprocal Transverse Magnetic (“TM”) mode converters, reciprocal TE mode converters and reciprocal TM mode converters, an absorption element to absorb modes of light of a particular polarization, and a space periodic magnetic field for quasi-phase match between TE and TM modes. This phase match requirement of conventional optical isolators with their light source, such as a semiconductor laser, is particularly difficult and problematic, and imposes severe fabrication tolerances. For example, the fabrication tolerances on such variables as composition, layer thickness, and interaction length are extremely difficult to consistently achieve and replicate. This causes reliability and performance concerns, along with significantly increased overall costs.
The increased use of semiconductor optical elements and devices, such as semiconductor lasers, laser arrays, and optical amplifiers, has resulted in the need to interface conventional optical isolators with such semiconductor optical elements and devices. This has presented serious challenges and problems. The dramatically different fabrication techniques and materials used in semiconductor optical elements and conventional optical elements and devices has made integration of these optical elements and devices either impossible or impractical.